Device for restoring cathode emission in cathode-ray tube guns

ABSTRACT

The heater filaments of the cathode-ray guns of a color television picture tube are connected across the low-voltage secondary winding of a transformer, the primary of which is connected across the terminals of a conventional household alternating current supply through a thermistor to effect gradual increase of potential across the secondary winding. As the filament voltage increases to normal operating potential, the degree of intensity of the lamps indicates the relative electron emission of the cathodes. As the filament voltage increases above normal operating potential, the temperature of the filament and cathode are increased above normal to effect progressive removal of contaminating materials from the cathodes. The cathodes are connected to one terminal of the alternating current supply and the control grids are connected to the other terminal of the alternating current supply each through a dropping resistance, circuit breaker and indicator lamp, to produce a pulsating direct current which effects progressive drawing of fresh electron emissive material to the surface of the cathodes. This automatic progressive restoration of the cathode is evidenced by progressive brightening of the lamps and when restoration of each cathode is completed, the associated circuit breaker opens automatically to terminate the treatment.

United States Patent Badewitz Feb. 8, 1972 [54] DEVICE FOR RESTORINGCATHODE EMISSION IN CATHODE-RAY TUBE GUNS [72] Inventor: AlbertBadewitz, Vancouver, Wash.

[73] Assignee: Beltron, Inc., Vancouver, Wash.

[22] Filed: June 6, 1969 [211 Appl. No.: 842,073

Primary Examinerlohn F. Campbell Assistant ExaminerRichard BernardLazarus Attorney0liver D. Olson [57] ABSTRACT The heater filaments ofthe cathode-ray guns of a color television picture tube are connectedacross the low-voltage secondary winding of a transformer, the primaryof which is connected across the tenninals of a conventional householdalternating current supply through a thermistor to effect gradualincrease of potential across the secondary winding. As the filamentvoltage increases to normal operating potential, the degree 'ofintensity of the lamps indicates the relative electron emission of thecathodes. As the filament voltage increases above normal operatingpotential, the temperature of the filament and cathode are increasedabove normal to effect progressive removal of contaminating materialsfrom the cathodes. The cathodes are connected to one terminal of thealternating current supply and the control grids are connected to theother terminal of the alternating current supply each through a droppingresistance, circuit breaker and indicator lamp, to produce a pulsatingdirect current which efiects progressive drawing of fresh electronemissive material to the surface of the cathodes. This automaticprogressive restoration of the cathode is evidenced by progressivebrightening of the lamps and when restoration of each cathode iscompleted, the associated circuit breaker opens automatically toterminate the treatment.

10 Claims, 1 Drawing Figure PATENTEDFEB 81872 ALBERT R. BADEWITZINVENTOR.

AGENT.

BACKGROUND OF THE INVENTION Restoration of cathode emission ofcathode-ray tubes, and 5 particularly television picture tubes,heretofore has involved the application of high-voltage direct currentacross the cathode and control grid for one or more short intervals oftime. There are many disadvantages in such procedure: The application ofhigh voltage direct current effects such a large rush of electrons fromthecathode that an excessive amount of the barium oxide or otherelectron emissive cathode material is removed with the contaminants. Theresulting improvement therefore is of short duration and the tubeusually is destroyed after a single treatment.

The application of high-voltage direct current also is capable ofproducing an electrical short between the cathode and control grid.Accordingly, in those very frequent instances in which a short isproduced during normal operation of the tube by expansion of themetallic elements during heating, the application of high-voltage directcurrent almost always insures the production of a permanent short bywelding the elements together.

Additionally, costly equipment is required to provide such high-voltagedirect current, and expert personnel is needed to operate such equipmentsince it requires the critical supervision of electrical quantitiesappropriate to the various types of cathode-ray tubes.

Further, such equipment is operable only upon one cathode-ray tube gunat a time. The restoration of cathodes of color television picture tubesthus involves the time required to process all three cathodes.

SUMMARY OF THE INVENTION In its basic concept the cathode emissionrestorer device of this invention applies to the filament of acathode-ray tube gun a voltage sufficient to heat it above normaloperating temperature, to effect release of contaminants from thecathode. The restorer device then utilizes the cathode and control gridof the cathode-ray tube being restored to rectify conventional householdalternating current to low-voltage pulsating direct current which isapplied across said cathode and control grid to increase electron flowfrom the cathode and effect consequent exposure of more barium oxide orother electron emissive material at the surface of the cathode.

It is by virtue of the foregoing basic concept that the principalobjective of this invention is achieved, namely to overcome the manydisadvantages of prior restoring devices, as enumerated hereinbefore.

Another object of this invention is to provide a device of the classdescribed which functions to restore cathode emission with minimum lossof electron emissive material, whereby restoration may be repeated manytimes and the useful life of the cathode-ray tube thus correspondinglyextended.

Another object of this invention is to provide a device of the classdescribed which is operable during the restoring operation automaticallyto repair electrical shorts which may exist between the cathode andcontrol grid.

Still another object of this invention is the provision of a device ofthe class described which is usable with cathode-ray tubes having one ora plurality of cathodes.

A further object of this invention is the provision of a device of theclass described which is operable with color television picture tubes torestore the emission quality of all three cathodes simultaneously.

A further objective of this invention is the provision of a device ofthe class described which is of simplified and inexpensive constructionand is automatic in operation, whereby it is available for purchase atreasonable cost and is usable effectively by home television owners forrepeated periodic restoration of television picture tubes.

The foregoing and other objects and advantages of this invention willappear from the following detailed description,

taken in connection with the accompanying drawing of the preferredembodiment.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is aschematic diagram of an electric circuit of a cathode emission restoringdevice embodying the features of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of illustration thedrawing shows a portion of a color television picture tube 10 whichincludes three color cathode-ray tube guns. Thus, there is shown thefilament I2, cathode l4 and control grid 16 of the greencolor.cathode-ray tube gun, the filament l8, cathode 20 and control grid22 of the red cathode-ray tube gun, and the filament 24, cathode 26 andcontrol grid 28 of the blue cathode-ray tube gun. These elements connectto corresponding pins (not shown) projecting from the base of the tube.Normally these pins are connected electrically to appropriate componentsof a television receiver through a complementary female connector.However, for purposes of this invention the conventional femaleconnector is removed and a substitute female connector 30 associatedwith the device of this invention is attached to the prns.

The electrical conductors leading from the female connector 30 arecarried in an elongated flexible cable of conventional construction. Thecable may be of any desired length to permit placement of the instrumentcase 32 of the device at a convenient location for use.

On the front panel of the case therc'are mounted three indicator lamps34, 36 and 38, preferably colored to correspond to the associated colorguns of the picture tube 10. A neon or other glow discharge tube 40 alsois mounted on the case. Projecting from the case are flexible electricalconductors providing the terminals 42 and 44 for connection to aconventional household supply of 1 lO-volt alternating current.

Within the case is mounted an alternating current stepdown transformer46. The opposite ends of the primary winding 48 of the transformer areconnected to the terminals 42 and 44, one through a thermistor S0. Theopposite ends of the secondary winding 52 of the transformer areconnected through conductors 54 and 56 to the opposite ends of thefilaments of the cathode-ray tube. Although the filaments are shownconnected together in series, it will be understood that they may beconnected in parallel.

The function of the thermistor is to increase the voltage to thefilaments slowly to a value greater than normal operating potential, soas to prevent damage to the filament. In this regard, the thermistor maybe replaced by a surgister, or by a rheostat or similar device, placedeither in the primary or secondary circuit. Alternatively, the secondarywinding may be provided with multiple taps selectable by a conventionalmultiple position switch.

The cathodes are connected in parallel through conductor 58 to terminal44 of the alternating current supply. The control grids are connected inparallel to the other terminal 42, each through a series arrangement ofone of the indicator lamps, a circuit breaker 60 and a voltage droppingresistor 62. The cathode and control grid of each gun thus is connectedacross the terminals 42, 44 of the alternating current supplyselectively through its associated circuit breaker. When all of thecircuit breakers are in their normally closed position, the cathode andcontrol grid of all three guns are connected simultaneously across thesupply terminals.

The circuit breakers 60 function to open each cathode and control gridcircuit when current flow reaches a predetermined value, as explainedhereinafter. The dropping resistors 62 serve to lower the voltage ineach cathode and control grid circuit to a desired level, for exampleabout 50 volts.

Means also is provided for indicating conveniently the existence of ashort between the heater filament and cathode of each gun. This isprovided by the neon or other glow discharge tube 40 which is connectedacross the common conductors 56 and 58 leading from the filaments andcathodes. The dropping resistor 64 connects the tube across the supplyterminals 42, 44.

The operation of the device described hereinabove is as follows:

Assuming it is desired to restore electron emission of the cathodes of acolor television picture tube, the female connector normally associatedwith the tube is removed and replaced by the adapter 30 associated withthe restoring device. In this regard it will be understood that thedevice will be provided with a number of adapters to accommodateconnection to the various types of picture tubes in use.

With the primary winding 48 of the transformer connected to thealternating current supply, through the terminals 42 and 44, the voltageacross the primary winding 50, and hence the secondary winding 52,gradually is increased by operation of the thermistor 50. As the lowvoltage applied to the filaments increases to normal filament operatingpotential, and with the circuit breakers 60 in their normally closedposition, the absence of, or only faint illumination from, the indicatorlamps gives automatic indication that electron emission from thecathodes is below normal. This would confirm the lack of properbrightness and contrast on the screen of the picture tube.

The thermistor 50 operates to increase the voltage to the filamentsslowly to a value greater than normal operating potential. Usually thispotential is not substantially greater than twice the normal operatingpotential. in any event it is not sufficient to burn out or otherwisedamage the filaments. However, this higher than normal filamentpotential causes the filaments to be heated to a temperature higher thannormal, to effect automatic removal of contaminants from the cathode.

Simultaneously with the application of filament potential, alternatingcurrent from the supply terminals 42, 44 is applied across the cathodeand control grid of each of the color guns. Each cathode and controlgrid functions to rectify this alternating current, to produce apulsating direct current at the frequency of the alternating currentsupply. The pulsating direct current flowing from the cathode to thecontrol grid has the effect of automatically drawing to the surface ofthe cathode molecules of barium oxide or other electron emissivesubstance of which the cathode is made.

The foregoing restoration process progresses over a period of time,depending upon the degree of contamination of the cathodes and themagnitude of potentials applied to the filaments and across the cathodesand control grids of the color guns. In any event, visual evidence ofthis progress is provided automatically by the indicator lamps whichincrease progressively in brightness. Color balance between all guns ofthe picture tube thus is afforded by visual comparison of brightness ofthe lamps. If desired, the lamps may be replaced by indicating meters.

Automatic termination of the restoration process is provided by thecircuit breakers 60. These are chosen to open when current flow reachesa magnitude corresponding to the desired degree of electron flow fromthe cathodes being restored.

In the event restoration of electron emission of one gun is completedbefore another, the circuit breaker associated with the completed gunwill open, allowing the restoration process to proceed automatically onthe other guns.

It will be apparent that the circuit breakers may be omitted and thatany desired circuit may be opened manually simply by unscrewing theassociated indicator lamp. Alternatively, the circuit breakers may bereplaced by on-off switches for manual operation.

Simultaneously with the restoration process the pulsating direct currentflowing from the cathode to the control grid of a gun has the effect ofautomatically repairing any electrical short that might exist betweenthe cathode and the control grid. Such shorts generally occur uponheating of the elements, which heating tends to expand the elements intophysical contact. However, as the elements approach mutual contact thepulsating direct current arcs across the elements and automaticallyburns away sufficient material to eliminate the short. The effect ofthis pulsating direct current is different from the effect of a steadydirect current which, under the same circumstances, effects weldingtogether of the elements.

The operation of the pulsating direct current to effect repair ofelectrical shorts between the cathode and control grid is automatic, aswill be apparent, and will occur without the knowledge of the operatorof the device.

lf an electrical short between the cathode and control grid exists atthe time the device is applied, the associated circuit breaker will opento indicate it. If the circuit breaker is not employed, the indicatorlamp will burnout, since it acts as a current limiting device or fuse.

Simultaneously with the testing and restoring procedure, visualindication is given automatically of the existence of an electricalshort between a filament and cathode,.by extinguishing of the neon lamp40. Correction of this problem generally is made by use of an isolationtransformer to separate the filament supply of the picture tube from thefilament supply of the other tube components in the television receiver.

The restoring device described hereinbefore also may be used to restoreelectron emission of the single cathode of a black and white televisionpicture tube. In such instance the device is connected to the picturetube by the use of an appropriate adapter 30 which connects the filamentto the secondary winding of the transformer, the cathode to one terminalof the alternating current supply and the control grid to the otherterminal of the supply through one of the series arrangements ofindicator lamp, circuit breaker and dropping resistance. The procedurefor checking and restoring electron emission is the same as describedhereinbefore.

It will be apparent that various changes may be made in the size,number, type and arrangement of parts described hereinbefore withoutdeparting from the spirit of this invention.

Having now described my invention and the manner in which it may beused, I claim:

1. A device for restoring electron emission of the cathode of a cathoderay tube gun having a filament, a cathode and a control grid, the devicecomprising a. a low-voltage electric circuit arranged for connectingacross the filament of the cathode-ray tube a voltage greater thannormal filament operating potential, the lowvoltage circuit includingvoltage control means for increasing the voltage to the filament fromnormal operating potential to said greater than normal potential,

b. an alternating current circuit arranged for connecting a source ofalternating current not exceeding about llO volts across the cathode andcontrol grid of the cathoderay tube, and

. electrical indicator means removably connected in said alternatingcurrent circuit for indicating and interrupting the flow of electronsfrom the cathode to the control grid of the cathode-ray tube.

2. The device of claim 1 wherein the indicator means is an electriclamp.

3. The device of claim 1 including circuit breaker means in saidalternating current circuit for opening the latter automatically uponattainment of a predetermined current flow through said circuit.

4. The device of claim 1 including means operatively associated with thelow-voltage electric circuit for connecting across the filament of thecathode-ray tube normal filament operating potential for testing themagnitude of electron flow from the cathode to the control grid prior toapplying said greater filament voltage.

5. The device of claim 1 wherein the low-voltage electric circuitcomprises the secondary winding of a transformer, the primary winding ofwhich is connected to said source of alternating current.

6. The device of claim 1 including electric indicator meansinterconnecting the low-voltage and alternating current circuits forconnection across the filament and cathode of a cathode-ray tube forindicating an electrical short therebetween.

7. The device of claim 1 for restoring simultaneously electron emissionof the cathodes of a plurality of cathode-ray guns of a color televisionpicture tube, wherein the alternating current circuit includes means forconnecting the cathodes and control grids of the plurality of gunssimultaneously across the alternating current supply, and the indicatormeans comprises an electric lamp for each gun.

8. The device of claim 7 wherein each lamp corresponds in color to thecolor provided by its associated gun.

9. The device of claim 8 including circuit breaker means in the circuitof each cathode and control grid for opening said circuit automaticallyupon attainment of a predetermined current flow through said circuit.

10. A device for restoring electron emission of the cathodes of aplurality of cathode-ray tube guns of a color television picture tubewherein each gun has a filament, a cathode and a control grid, thedevice comprising:

a. a filament voltage circuit arranged for connecting across thefilaments of the guns a voltage greater than normal filament operatingpotential, and including voltage control means for increasing thevoltage to the filaments from normal operating potential to the greaterthan normal potential,

b. an electric circuit arranged for connecting a source of electricpotential not exceeding about volts across the cathode and control gridof each gun, and

c. electrical indicator means removably connected in the cathode andcontrol grid circuit of each gun for indicating and interrupting theflow of electrons therebetween.

1. A device for restoring electron emission of the cathode of a cathoderay tube gun having a filament, a cathode and a control grid, the devicecomprising a. a low-voltage electric circuit arranged for connectingacross the filament of the cathode-ray tube a voltage greater thannormal filament operating potential, the low-voltage circuit includingvoltage control means for increasing the voltage to the filament fromnormal operating potential to said greater than normal potential, b. analternating current circuit arranged for connecting a source ofalternating current not exceeding about 110 volts across the cathode andcontrol grid of the cathode-ray tube, and c. electrical indicator meansremovably connected in said alternating current circuit for indicatingand interrupting the flow of electrons from the cathode to the controlgrid of the cathode-ray tube.
 2. The device of claim 1 wherein theindicator means is an electric lamp.
 3. The device of claim 1 includingcircuit breaker means in said alternating current circuit for openingthe latter automatically upon attainment of a predetermined current flowthrough said circuit.
 4. The device of claim 1 including meansoperatively associated with the low-voltage electric circuit forconnecting across the filament of the cathode-ray tube normal filamentoperating potential for testing the magnitude of electron flow from thecathode to the control grid prior to applying said greater filamentvoltage.
 5. The device of claim 1 wherein the low-voltage electriccircuit comprises the secondary winding of a transformer, the primarywinding of which is connected to said source of alternating current. 6.The device of claim 1 including electric indicator means interconnectingthe low-voltage and alternating current circuits for connection acrossthe filament and cathode of a cathode-ray tube for indicating anelectrical short therebetween.
 7. The device of claim 1 for restoringsimultaneously electron emission of the cathodes of a plurality ofcathode-ray guns of a color television picture tube, wherein thealternating current circuit includes means for connecting the cathodesand control grids of the plurality of guns simultaneously across thealternating current supply, and the indicator means comprises anelectric lamp for each gun.
 8. The device of claim 7 wherein each lampcorresponds in color to the color provided by its associated gun.
 9. Thedevice of claim 8 including circuit breaker means in the circuit of eachcathode and control grid for opening said circuit automatically uponattainment of a predetermined current flow through said circuit.
 10. Adevice for restoring electron emission of the cathodes of a plurality ofcathode-ray tube guns of a color television picture tube wherein eachgun has a filament, a cathode and a control grid, the device comprising:a. a filament voltage circuit arranged for connecting across thefilaments of the guns a voltage greater than normal filament operatingpotential, and including voltage control means for increasing thevoltage to the filaments from normal operating potential to the greaterthan normal potential, b. an electric circuit arranged for connecting asource of electric potential not exceeding about 110 volts across thecathode and control grid of each gun, and c. electrical indicator meansremovably connected in the cathode and control grid circuit of each gunfor indicating and interrupting the flow of electrons therebetween.